In a power semiconductor module, with an increase in current capacity and a reduction in the size of the power semiconductor module, a semiconductor chip is used at high current density. Therefore, it is important to effectively dissipate the heat generated from the semiconductor chip in order to ensure reliability during a high-power operation.
FIGS. 9 to 12 are cross-sectional views illustrating production processes of a method for producing a main portion of a power semiconductor module according to the related art.
In FIG. 9, solder 52 is provided on a heat dissipating base 51 and an insulating substrate 69 with a conductive pattern is provided on the solder 52. In the insulating substrate 69 with a conductive pattern, a rear conductive film 53 is formed on the rear surface of an insulating substrate 54 which is made of, for example, ceramic and a conductive pattern 55 is formed on the front surface thereof. Then, solder 56 is provided on the conductive pattern 55 of the insulating substrate 69 with a conductive pattern. An IGBT chip 57a is provided on the solder 56, with a collector electrode (not illustrated) down, and an FWD chip 57b is provided on the solder 56, with a cathode electrode (not illustrated) down. Then, solder 58 is provided on an emitter electrode (not illustrated) of the IGBT chip 57a and an anode electrode (not illustrated) of the FWD chip 57b. Then, an emitter lower terminal 60 is provided on the solder 58. In addition, solder 59 is provided on the conductive pattern 55 of the insulating substrate 69 with a conductive pattern and a collector lower terminal 61 is provided on the solder 59. Then, in this state, heat is applied to melt the solders 52, 56, 58, and 59 and the solders 52, 56, 58, and 59 are cooled and re-solidified such that the members are fixed and integrated by the solders 52, 56, 58, and 59. Here, the solder before it is melted, and the solder while it is being melted, and the solder after it is solidified are denoted by the same reference numeral.
Then, in FIG. 10, a resin case 64 having the emitter upper terminal 62 and the collector upper terminal 63 formed integrally therewith is covered and the lower portion of the resin case 64 is fitted to an outer circumferential portion of the heat dissipating base 51. An adhesive 65 for adhesion to the heat dissipating base 51 is applied to the lower portion of the resin case 64.
Then, in FIG. 11, the adhesive 65 is heated and hardened to fix the resin case 64 and the heat dissipating base 51. In this case, the opposite surfaces of the emitter upper terminal 62 and the emitter lower terminal 60 close contact each other and the opposite surfaces of the collector upper terminal 63 and the collector lower terminal 61 close contact each other. A laser beam 67 is radiated to the surfaces of the emitter upper terminal 62 and the collector upper terminal 63. With this irradiation, the laser beam 67 is absorbed by the outermost surfaces of the upper terminals 62 and 63 and is then converted into thermal energy. Then, each terminal is melted and a welded portion 66 is formed. Therefore, the upper and lower terminals 62 and 60 are fixed to each other by laser welding and the upper and lower terminals 63 and 61 are fixed to each other by laser welding.
Then, in FIG. 12, the resin case 64 is filled with a sealing material 68, such as silicon gel or epoxy resin, to complete a power semiconductor module.
In the process illustrated in FIG. 10, when a gap is formed between the upper and lower terminals 62 and 60, a load 73 is applied to remove the gap P such that the upper and lower terminals 62 and 60 contact each other, as illustrated in FIG. 13.
As such, when the upper and lower terminals 62 and 60 are fixed by laser welding while contacting each other, a variation in bonding strength occurs. Therefore, Patent Document 1 discloses a technique in which spacers 74 are provided between the opposite surfaces of the emitter upper terminal 62 and the emitter lower terminal 60 and between the opposite surfaces of the collector upper terminal 63 and the collector lower terminal 61 to form a gap M of about 10 μm therebetween and laser welding is performed for the upper and lower terminals, as illustrated in FIG. 14.